Frequently filters are simply changed on a set schedule regardless of their ongoing performance and/or remaining capacity. For example, the filters that are used in research buildings to filter hood exhausts are typically changed on a schedule regardless of remaining filter capacity. This approach may be inefficient in that filters may be changed prior to exhaustion and/or ineffective in that filters may be left in use beyond their actual ability to perform.
Determining the remaining life of a carbon air filter may be encumbered by a need to remove it from service. For example, upon removal of a filter from service, a carbon sample may be taken from the filter and properties of the carbon may be assessed in a lab. Or the selected filter itself may be challenged with a probe chemical until the filter life is reached. For example, a pulse of adsorbing gas may be introduced into the system and the time necessary for the pulse to exit the filter assessed. In either case, the filter must be removed from the filter housing and probed. A war-fighter, for example, may lack a quick, on-site, means of assessing the level of protection remaining in his collective protection system. Assessing filter performance may be costly (e.g., for filter down time, analytic reagents, and/or dedicated lab facilities needed) and may still fall short of delivering real time assessments of performance and/or remaining filter life.